#include "UiSurface.hpp"

#include <cmath>

#include "UiLayout.hpp"

namespace jdi
{

	UiSurface UiSurface::SubView(const gd::RectF& localRect) const
	{
		UiSurface view;
		if (!Valid())
		{
			return view;
		}
		// 子矩形先换算到宿主坐标，再夹在本表面之内：超出本表面的部分没有属于它的像素，
		// 若照原样返回 `bits` 偏移会写到相邻区域（典型的"子控件涂到别人身上"）。
		const gd::RectF requested(rect.X + localRect.X, rect.Y + localRect.Y, localRect.Width,
		                          localRect.Height);
		gd::RectF clamped;
		if (!UiRectIntersect(rect, requested, clamped))
		{
			return UiSurface();
		}

		view.dc = dc;
		view.rect = clamped;
		view.stride = stride;
		view.version = version;
		view.scale = scale;
		if (bits != nullptr && stride > 0)
		{
			const int offsetX = static_cast<int>(std::lround(clamped.X - rect.X));
			const int offsetY = static_cast<int>(std::lround(clamped.Y - rect.Y));
			view.bits = bits + static_cast<std::ptrdiff_t>(offsetY) * (stride / 4) + offsetX;
		}
		return view;
	}

} // namespace jdi